THz EPR-on-a-Chip for Enhanced Spin Sensitivity

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Electron paramagnetic resonance (EPR) is amongst the most powerful analysis methods in chemistry, physics, medicine, and materials science. It utilizes radical electron spins as probes to resolve the structure-function relationship of complex materials and interfaces. Unfortunately, EPR’s broad application potential is offset by very high instrumentation costs, moderate sensitivity, and insufficient flexibility in the sample environment due to the conventionally used resonator-based measurement principle. The proposed project aims at overcoming the aforementioned limitations of EPR by extending the recently introduced EPR-on-a-chip (EPRoC) approach, which integrates the entire spin excitation source and detector onto a single integrated circuit, from the GHz into the THz regime. Overall, the new THz EPRoC spectrometer that will emerge from the project will greatly reduce the experimental complexity of THz EPR and, at the same time, provide unprecedented sensitivity and spectral resolution, being at least two orders of magnitude better than GHz EPRoC. To this end, we will both theoretically research and experimentally investigate a new class of voltage-controlled oscillators (VCOs) that make use of split inductors as THz magnetic field sources and EPR detectors. Within the project, we will apply this new THz technology to study defects located in the interface region of the high-efficiency crystalline silicon single junction and tandem perovskite solar cells with an amorphous silicon selective contact layer. Here, we will achieve an unprecedented sensitivity of only a few hundred defects by detecting the paramagnetic defects as a magnetic fingerprint in the solar cell’s current, both under ambient operating conditions and at liquid helium temperatures. The project will demonstrate the immense application potential of THz EPRoC spectroscopy and will help to pave the technological road for a broad application of THz EPR spectroscopy in materials science, analytical chemistry, and biomedical research.